From the Super Mario Wiki
Final Showdown is the final quest of Mario Party Advance. It can only be initiated once all forty-eight other quests have been completed. It takes place at the Pipe House, behind the large wall with Bowser's logo, and it starts after Bowser challenges the player to see if they can win the final Gaddget. The player has the option to ask what Bowser is talking about, which leaves him and Koopa Kid confused and dejected that they didn't battle, though agreeing to the challenge is the only way to start the quest. Once the challenge is accepted, Bowser presents the Trap Floor minigame for the player to complete. If the player loses, Bowser expresses his disappointment with the player and forces them back to the Pipe House's entrance (notably, the player does not lose a Mushroom). If the player wins, Bowser is glad to have a worthy rival and rewards them with the Bowser Print Gaddget, telling the player that he wants to battle them again the future. Afterwards, a credits sequence featuring every inhabitant of Shroom City plays, letting the player know what happened to them through short descriptions. The quest ends once the final character, Bowser, scrolls away.
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